Typically, a Winchester-type disc drive is comprised of: one or more discs attached to a spindle motor such that the motor rotates the disc at a proscribed rate; an actuator assembly (also known as a transducer positioner assembly) including a read/write transducer assembly, a pivot, and a voice coil motor (VCM) to cause the assembly to pivot and position the transducer assembly over the discs; and a frame by which the pivot, VCM and the spindle motor are supported. As is well known in the art, a number of transducers may be mounted upon a single actuator assembly in order to access information on several stacked rotating discs. Various sorts of electronics to read and write data from and to the transducers, control the speed of the spindle motor, and control the position of the actuator assembly relative to the disc are also present in a typical disc drive.
During normal operation the transducers, also known in the art as heads, "float" above the disc surface accessing the information magnetically stored on the disc (reading) or placing new information on the disc (writing). The rotation of the disc causes air currents which create an "air bearing" to support the transducers above the disc surface. However, when the disc stops spinning, the air bearing ceases to exist, and without taking precautions, the transducers will impact the disc surface. Consequently, serious damage can result to the disc surface as the transducers come to rest on the disc surface. Therefore, much research has been focused upon methods to move the actuator assembly to park the transducer away from the disc surface prior to powering down the disc drive.
An orderly power down provides ample notice for the disc drive electronics to command the actuator assembly to a parked position. However, unscheduled power downs, such as occur during power outages, present a different problem since the internal electronics will not have sufficient time to park the actuator. For these instances, an automatic parking system that is activated when power is lost is desirable.
Typically, the parking is accomplished by pivoting the actuator arm portion which carries the transducers away from the discs to contact a latching means for maintaining the actuator arm portion in a fixed, parked position. The latching means is typically a ramp member, but may be a magnetic latch, mechanical latch, or some combination of mechanical and electrical apparatus.
To facilitate parking, the transducers are attached to a flexible portion or flexure which slides up the ramp member distancing the transducers from the disc. The ramp member supports the flexure and ensures that the transducers cannot impact the disc surface during shipping and other situations involving rough handling while the power is off.
The problem facing designers is how to move the flexure up the ramp member, or into contact with other forms of latches, when external power has been disconnected. One example of generating power to accomplish the parking procedure uses the kinetic energy (back-EMF) of the spindle motor as it spins to a stop after the power has been extinguished. By rectifying the back-EMF voltage from the spindle motor, a sufficient voltage is generated to enable power to be applied to the actuator assembly's voice coil motor, pivot the assembly, and drive the flexure onto the ramp or into contact with other latch means. However, this method necessitates using a complex arrangement of switching, impedance matching, and back-EMF rectification circuitry. Additionally, to facilitate the utilization of as much generated power as possible, the circuits are constructed from costly low loss components.
In addition to protecting the transducers by parking the actuator assembly, apparatus must be provided to ensure that the actuator assembly cannot excessively rotate about its pivot and cause the transducers to impact the hub to which the disc is mounted. Impact with the hub may cause severe damage to the transducers. To limit the actuator arm's motion a crash stop is usually provided. Typically, a crash stop is a metal flange having a piece foam rubber attached to it to partially absorb the shock of impact. In operation, the arm will impact the crash stop and cease rotation when the transducer is near the hub. Though effective in stopping the transducers from impacting the hub, the shock associated with a mechanical crash stop can cause misalignment of the heads or unbalance the bearings which support the actuator arm at the pivot.
An object of the present invention is to provide a simple apparatus to aid in parking the actuator assembly. The simplicity of the invention will result in lower overall disc drive manufacturing costs.
Accordingly, it is a primary objective of the present invention to provide an effective head positioning assembly latching and crash stop arrangement that has a low part count and is easy to assemble at low cost.
Another object of the present invention is to reduce the VCM torque requirement during normal parking maneuvers. The invention provides a supplemental force to move the flexure up the ramp, thus a less powerful and smaller VCM is possible.
Another object of the present invention is to reduce the spindle motor back-EMF requirement. In some applications, the present invention may not provide enough force to fully park the transducers. In these cases, the present invention will be used to supplement the rectified back-EMF power generation system. In doing so, the supplemental force will be large enough to enable the design to be accomplished without using low loss specialty components to rectify the back-EMF signals. More specifically, the approach taken in the present invention reduces the need for providing a motor with a high motor constant, an important advantage since the cost of a motor increases with need for a higher motor constant. Prior to the development of the present design, it was necessary to design the spindle motor with low motor resistance so that enough current was delivered to the voice coil when the only voltage source was back-EMF to drive it to the park position. With the supplemental driving force provided by the present invention, the design can tolerate a higher winding resistance in the spindle motor, and of course a higher resistance in the voice coil motor also, which reduces cost in one or both of the elements of primary expense in a disc drive design.
Another objective of the present invention is to provide a latch and crash stop arrangement which does not rely upon the impact of the moving actuator assembly to be effective.